765 research outputs found
Wound repair in sensory organs of the avian inner ear.
Hair cells are the sensory receptors of the inner ear, converting sound and accelerations into neuronal signals. Unlike mammals, birds are able to regenerate their sensory function after auditory or vestibular trauma. Sensory regeneration requires a composite programme of epithelial repair, hair cell production and functional reinnervation. The purpose of this thesis was to explore the mechanisms of epithelial repair in the avian inner ear, and examine their contribution within the broader process of sensory regeneration. An epithelial cell culture model of the chick utricle (Gallus gallus) was developed to facilitate in vitro experimentation. Initial investigations utilised laser ablation to create wounds in the sensory epithelium. Epithelial wounds were found to heal within 4 hours using a contractile acto-myosin cable in combination with lamellipodia driven cell crawling. Nuclear incorporation of BrdU was also used to assess support cell proliferation at the sites of epithelial wounds. Proliferation was significantly increased within 48 hours of laser ablation, and was spatially restricted to the areas of epithelial trauma. The increase was strongly reduced by pharmacological blockade of PI3K, but only partially so using inhibitors of the ERK and JNK MAP kinases. The response of the avian sensory epithelium to aminoglycoside ototoxicity has also been investigated. Streptomycin sulphate was used to induce extensive hair cell death in explant cultures of the chick utricle. During this process, support cells were found to remodel and eliminate the hair cell from the epithelial surface. Time-lapse microscopy of p-actin-EGFP revealed that support cells formed a cable of f-actin around the hair cell neck. The cable subsequently constricted to repair the epithelial defect, and in doing so severed and ejected the hair bundle. Support cells adjacent to a dying hair cell also extended pseudopodia basolaterally to form a distinctive calyx of f- actin around the soma. Simultaneous time-lapse recordings of p-actin-EGFP with TOTO-3 revealed that the support cell calyx was a phagocytic structure, which culminated in the engulfment of the hair cell. These results demonstrated that support cells have a proactive role in both maintenance of epithelial integrity and the removal of corpses during hair cell death
Sub-arcsecond radio and optical observations of the likely counterpart to the gamma-ray source 2FGL J2056.7+4939
We have searched and reviewed all multi- wavelength data available for the
region towards the gamma-ray source 2FGL J2056.7+4939 in order to con- strain
its possible counterpart at lower energies. As a result, only a point-like
optical/infrared source with flat-spectrum radio emission is found to be
consistent with all X-ray and gamma-ray error circles. Its struc- ture is
marginally resolved at radio wavelengths at the sub-arcsecond level. An
extragalactic scenario appears to be the most likely interpretation for this
object.Comment: 5 pages, 3 figures, 1 tabl
The Saffman-Taylor problem on a sphere
The Saffman-Taylor problem addresses the morphological instability of an
interface separating two immiscible, viscous fluids when they move in a narrow
gap between two flat parallel plates (Hele-Shaw cell). In this work, we extend
the classic Saffman-Taylor situation, by considering the flow between two
curved, closely spaced, concentric spheres (spherical Hele-Shaw cell). We
derive the mode-coupling differential equation for the interface perturbation
amplitudes and study both linear and nonlinear flow regimes. The effect of the
spherical cell (positive) spatial curvature on the shape of the interfacial
patterns is investigated. We show that stability properties of the fluid-fluid
interface are sensitive to the curvature of the surface. In particular, it is
found that positive spatial curvature inhibits finger tip-splitting. Hele-Shaw
flow on weakly negative, curved surfaces is briefly discussed.Comment: 26 pages, 4 figures, RevTex, accepted for publication in Phys. Rev.
In-Situ Nuclear Magnetic Resonance Investigation of Strain, Temperature, and Strain-Rate Variations of Deformation-Induced Vacancy Concentration in Aluminum
Critical strain to serrated flow in solid solution alloys exhibiting dynamic strain aging (DSA) or Portevin–LeChatelier effect is due to the strain-induced vacancy production. Nuclear magnetic resonance (NMR) techniques can be used to monitor in situ the dynamical behavior of point and line defects in materials during deformation, and these techniques are nondestructive and noninvasive. The new CUT-sequence pulse method allowed an accurate evaluation of the strain-enhanced vacancy diffusion and, thus, the excess vacancy concentration during deformation as a function of strain, strain rate, and temperature. Due to skin effect problems in metals at high frequencies, thin foils of Al were used and experimental results correlated with models based on vacancy production through mechanical work (vs thermal jogs), while in situ annealing of excess vacancies is noted at high temperatures. These correlations made it feasible to obtain explicit dependencies of the strain-induced vacancy concentration on test variables such as the strain, strain rate, and temperature. These studies clearly reveal the power and utility of these NMR techniques in the determination of deformation-induced vacancies in situ in a noninvasive fashion.
Density-functional embedding using a plane-wave basis
The constrained electron density method of embedding a Kohn-Sham system in a
substrate system (first described by P. Cortona, Phys. Rev. B {\bf 44}, 8454
(1991) and T.A. Wesolowski and A. Warshel, J. Phys. Chem {\bf 97}, 8050 (1993))
is applied with a plane-wave basis and both local and non-local
pseudopotentials. This method divides the electron density of the system into
substrate and embedded electron densities, the sum of which is the electron
density of the system of interest. Coupling between the substrate and embedded
systems is achieved via approximate kinetic energy functionals. Bulk aluminium
is examined as a test case for which there is a strong interaction between the
substrate and embedded systems. A number of approximations to the
kinetic-energy functional, both semi-local and non-local, are investigated. It
is found that Kohn-Sham results can be well reproduced using a non-local
kinetic energy functional, with the total energy accurate to better than 0.1 eV
per atom and good agreement between the electron densities.Comment: 11 pages, 4 figure
The Physics of turbulent and dynamically unstable Herbig-Haro jets
The overall properties of the Herbig-Haro objects such as centerline
velocity, transversal profile of velocity, flow of mass and energy are
explained adopting two models for the turbulent jet. The complex shapes of the
Herbig-Haro objects, such as the arc in HH34 can be explained introducing the
combination of different kinematic effects such as velocity behavior along the
main direction of the jet and the velocity of the star in the interstellar
medium. The behavior of the intensity or brightness of the line of emission is
explored in three different cases : transversal 1D cut, longitudinal 1D cut and
2D map. An analytical explanation for the enhancement in intensity or
brightness such as usually modeled by the bow shock is given by a careful
analysis of the geometrical properties of the torus.Comment: 17 pages, 10 figures. Accepted for publication in Astrophysics &
Spac
Origins of the Ambient Solar Wind: Implications for Space Weather
The Sun's outer atmosphere is heated to temperatures of millions of degrees,
and solar plasma flows out into interplanetary space at supersonic speeds. This
paper reviews our current understanding of these interrelated problems: coronal
heating and the acceleration of the ambient solar wind. We also discuss where
the community stands in its ability to forecast how variations in the solar
wind (i.e., fast and slow wind streams) impact the Earth. Although the last few
decades have seen significant progress in observations and modeling, we still
do not have a complete understanding of the relevant physical processes, nor do
we have a quantitatively precise census of which coronal structures contribute
to specific types of solar wind. Fast streams are known to be connected to the
central regions of large coronal holes. Slow streams, however, appear to come
from a wide range of sources, including streamers, pseudostreamers, coronal
loops, active regions, and coronal hole boundaries. Complicating our
understanding even more is the fact that processes such as turbulence,
stream-stream interactions, and Coulomb collisions can make it difficult to
unambiguously map a parcel measured at 1 AU back down to its coronal source. We
also review recent progress -- in theoretical modeling, observational data
analysis, and forecasting techniques that sit at the interface between data and
theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue
connected with a 2016 ISSI workshop on "The Scientific Foundations of Space
Weather." 44 pages, 9 figure
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